Miscut bulk substrates

ABSTRACT

A method for providing (Al,Ga,In)N thin films on Ga-face c-plane (Al,Ga,In)N substrates using c-plane surfaces with a miscut greater than at least 0.35 degrees toward the m-direction. Light emitting devices are formed on the smooth (Al,Ga,In)N thin films. Devices fabricated on the smooth surfaces exhibit improved performance.

This application claims the benefit of U.S. Provisional Application No.61/470,901 filed on Apr. 1, 2011, which is incorporated by referenceherein in its entirety.

BACKGROUND

The present disclosure is directed to fabrication of optical devices.More particularly, the disclosure provides methods and devices using amiscut (Al,Ga,In)N bulk crystal. Certain embodiments provided by thedisclosure include techniques for fabricating light emitting devicesusing miscut gallium nitride containing materials. Such devices can beapplied to applications such as optoelectronic devices. In certainembodiments, the disclosure provides methods of manufacture using anepitaxial gallium containing crystal with extremely smooth surfacemorphology and uniform wavelength over a large surface area of thesubstrate. Such crystals and materials include GaN, AlN, InN, InGaN,AlGaN, and AlInGaN, for manufacture of bulk or patterned substrates.

In the late 1800's, Thomas Edison invented the light bulb. Theconventional light bulb, commonly called the “Edison bulb,” has beenused for over one hundred years. The conventional light bulb uses atungsten filament enclosed in a glass bulb sealed in a base, which isscrewed into a socket. The socket is coupled to an AC power or DC powersource. The conventional light bulb can be found commonly in houses,buildings, and outdoors. Unfortunately, the conventional light bulbdissipates more than 90% of the energy used as thermal energy.Additionally, the light bulb eventually fails due to evaporation of thetungsten filament.

Fluorescent lighting uses an optically clear tube filled with a noblegas, and typically also contains mercury. A pair of electrodes iscoupled to an alternating power source through a ballast. Once themercury has been excited, it discharges to emit UV light. Typically, thetube is coated with phosphors, which are excited by the UV light toprovide white light. Recently, fluorescent lighting has been fitted ontoa base structure to couple into a standard socket.

Solid state lighting relies upon semiconductor materials to producelight emitting diodes, commonly called LEDs. At first, red LEDs weredemonstrated and introduced into commerce. Modern, red LEDs use aluminumindium gallium phosphide or AlInGaP semiconductor materials. Mostrecently, Shuji Nakamura pioneered the use of InGaN materials to produceLEDs emitting light in the blue range for blue LEDs. Blue LEDs led toinnovations in lighting, and the blue laser diode enabled DVD players,and other developments. Blue, violet, or ultraviolet-emitting devicesbased on InGaN are used in conjunction with phosphors to provide whiteLEDs.

BRIEF SUMMARY

This disclosure generally relates to manufacture of materials anddevices. More particularly, the disclosure provides methods and devicesusing a miscut (Al,Ga,In)N bulk crystal. Certain embodiments provided bythe disclosure include techniques for fabricating light emitting devicesand/or electronic devices using miscut gallium nitride containingmaterials. Devices provided by the present disclosure can be applied toapplications such as optoelectronic devices. In certain embodiments, thedisclosure provides methods of manufacture using a high qualityepitaxial gallium containing crystal with extremely smooth surfacemorphology and uniform wavelength across a large surface area of thesubstrate. Such crystals and materials include GaN, AlN, InN, InGaN,AlGaN, and AlInGaN, for manufacture of bulk or patterned substrates.

Certain embodiments provided by the present disclosure include methodsfor processing and utilizing bulk substrates. Certain methods includefabricating at least one (Al,Ga,In)N thin film directly on a (Al,Ga,In)Nsubstrate or template. The substrate or template has a surfacecharacterized by a miscut angle of at least 0.35 degrees toward them-direction, and the projection of the surface normal coincides with them-axis. The substrate or template can be obtained by slicing a c-planewafer at a predetermined miscut angle of at least 0.35 degrees relativeto c-plane toward or away from the m-direction.

In certain embodiments, the present disclosure provides methods formanufacturing optical devices from a bulk substrate material, such as abulk gallium and nitrogen containing substrate material, for example,GaN. Methods include providing a bulk gallium and nitrogen containingsubstrate material having a top surface. At least one surface region onthe top surface of the bulk gallium and nitrogen containing substratehas a miscut angle of at least 0.35 degrees toward the m-direction.Methods also include subjecting the surface region to a treatmentprocess to remove one or more areas with surface damage or sub-surfacedamage within the surface region. A treatment process can be a thermalprocess using a hydrogen and nitrogen bearing species. In certainembodiments, the method includes forming a n-type gallium and nitrogenmaterial (or undoped material) overlying the surface region and formingan active region from a stack of thin film layers. Each of the thin filmlayers may comprise an indium species, an aluminum species, and agallium and nitrogen containing species overlying the n-type gallium andnitrogen containing material. In certain embodiments, the methodincludes forming an aluminum gallium and nitrogen containing electronblocking material overlying the active region and forming a p-typegallium and nitrogen containing material overlying the electron blockingmaterial to cause formation of a processed gallium and nitrogencontaining substrate. In certain embodiments, the processed bulk galliumand nitrogen containing substrate is characterized by aphotoluminescence (PL) wavelength standard deviation of 0.2% and less;and each of the thin film layers have a surface region characterized bya root mean squared (RMS) surface roughness of 0.3 nm and less over anarea of at least 2,500 μm².

In certain embodiments, a hydrogen bearing species and a nitrogenbearing species are derived from hydrogen gas and ammonia gas,respectively. In certain embodiments, a n-type gallium and nitrogencontaining material is n-type GaN. In certain embodiments, a p-typegallium and nitrogen containing material is p-type GaN. In certainembodiments, an electron blocking material is AlGaN. In certainembodiments, each of the thin film layers forming the active region isAlInGaN. In certain embodiments, the active layer comprises a pluralityof quantum wells, which comprise. for example, from three to twentyquantum wells. In certain embodiments, each of the quantum wells may beseparated by a barrier region. In certain embodiments, a barrier regioncomprises GaN.

In certain embodiments, the present disclosure provides methods forfabricating a device. Method include, for example, providing a galliumand nitrogen containing substrate having a surface region, which has ac-plane surface region characterized by a miscut angle of at least 0.35degrees from the c-plane toward the m-direction. In certain embodiments,the method includes forming a gallium and nitrogen containing thin filmcomprising an aluminum bearing species and an indium bearing species onthe gallium and nitrogen containing substrate. In certain embodiments,the methods include forming an electrical contact region overlying thethin film.

The disclosure provides ways for identifying and selecting portionsand/or regions of a substrate that are suitable for manufacturing LEDdiodes or other devices. Such regions are characterized by a miscutangle of at least 0.35 degrees toward the m-direction on a gallium andnitrogen containing substrate. Surprisingly, using miscut angles of atleast 0.35 degrees toward the m-direction improves consistency and yieldof processed devices. By having a miscut angle of at least 0.35 degreestoward the m-direction, or in certain embodiments, greater than 0.4degrees toward the m-direction and/or the a-direction, as opposed to alower miscut angle, the surface morphology of a substrate is improved ina way that is advantageous for manufacturing LED devices such that themanufacturing yield of the devices is increased and the performance isimproved. A miscut angle of at least 0.35 degrees toward the m-directionresults in a smooth substrate surface to improved device performance andreliability. One of the reasons for improved performance is that asmooth substrate surface results in high carrier mobility and lowerseries resistance. In addition, a smooth substrate surface reducesoptical scattering of optical devices formed on the substrate. Overall,improved PL performance is achieved using a miscut of at least 0.35degrees from a c-plane toward the m-direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a miscut map of a substrate (Substrate A) cut along them-direction. The values represent angles with respect to the c-plane.

FIG. 1B shows a miscut map of a substrate cut along the a-direction. Thevalues represent angles with respect to the c-plane

FIG. 2 shows photo luminescence (PL) maps for an InGaN/GaNheterostructure grown on the substrate of FIG. 1A and FIG. 1B.

FIG. 3 Nomarski images of the surface morphology of a grown on SubstrateA. The Nomarski images correspond to the relative position on SubstrateA illustrated on the left side of FIG. 3.

FIG. 4 shows atomic force microscopy (AFM) amplitude images of five 2×2μm² areas of Substrate A. The root-mean-square (RMS) average amplitudes(nm) are indicated for certain areas.

FIG. 5 shows atomic force microscopy (AFM) amplitude images of five50×50 μm² areas of Substrate A. The root-mean-square (RMS) averageamplitudes (nm) are indicated for certain areas.

FIG. 6A shows the crystallographic planes for a c-plane wafer miscuttoward the m-direction (m-axis).

FIG. 6D shows a cross-sectional view of a wafer depicting the relativeorientation of lattice planes with respect to the wafer surface for amiscut wafer.

FIG. 6C shows the crystallographic planes for a c-plane wafer miscuttoward the m-direction (m-axis) and toward the a-direction (a-axis).

FIG. 6B shows a cross-sectional view of a wafer depicting the relativeorientation of lattice planes with respect to the wafer surface for amiscut wafer.

FIG. 7 shows Nomarski images of the surface morphology of a c-planewafer miscut at angles of 0.14°, 0.23°, 0.31°, 0.36°, 0.41°, and 0.45°toward the m-direction.

FIG. 8 is a graph showing the relationship between miscut angle in them-direction and in the a-direction and RMS surface roughness.

FIG. 9 shows steps for growing an optical device according to certainembodiments provided by the present disclosure.

FIG. 10 shows steps for growing a rectifying p-n junction diodeaccording to certain embodiments provided by the present disclosure.

FIG. 11 shows steps for growing a high electron mobility transistor or ametal-semiconductor field effect transistor according to certainembodiments provided by the present disclosure.

DETAILED DESCRIPTION

Reference is now made to certain embodiments of polymers, compositions,and methods. The disclosed embodiments are not intended to be limitingof the claims. To the contrary, the claims are intended to cover allalternatives, modifications, and equivalents.

The present disclosure generally relates to the manufacture of materialsand devices. More particularly, the present disclosure provides methodsand devices using a miscut (Al,Ga,In)N bulk crystal. Certain embodimentsprovided by the present disclosure include techniques for fabricatinglight emitting devices using miscut gallium nitride containingmaterials. Devices provided by the present disclosure can be applied toapplications such as optoelectronic devices. In certain embodiments, thepresent disclosure provides methods of manufacture using an epitaxialgallium containing crystal having a smooth surface morphology anduniform wavelength across a large area of the substrate. Such crystalsand materials include GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and canbe used for the manufacture of bulk or patterned substrates. As usedherein, the term substrate also includes templates.

As background information, conventional GaN-based light emitting diodes(LED) emitting in the ultraviolet and visible regions are typicallybased on hetereoepitaxial growth where growth is initiated on asubstrate other than GaN such as sapphire, silicon carbide, or silicon.This is due to the limited supply and high cost of free-standing GaNsubstrates, which has prevented their viability for use in LEDmanufacture. However, the field of bulk-GaN technology has seen rapidgains over the past couple of years providing promise for large-scaledeployment into LED manufacture. Such a technology shift will providebenefits to LED performance and manufacturing.

Progress has been made during the past decade and a half in theperformance of gallium nitride-(GaN) based light emitting diodes.Devices with a luminous efficiency greater than 100 lumens per watt havebeen demonstrated in the laboratory, and commercial devices have anefficiency that is already considerably superior to that of incandescentlamps, and that is competitive with fluorescent lamps. Furtherimprovements in efficiency can reduce operating costs, reduceelectricity consumption, and decrease emissions of carbon dioxide andother greenhouse gases produced in generating the energy used forlighting applications.

Smooth morphology is important for high-quality crystal growth. Heavilydislocated films of GaN grown on sapphire, SiC, or other non-nativesubstrates have morphologies and growth conditions dictated by themicrostructure of the film. On the other hand, growth of GaN on nativebulk substrates is no longer heavily mediated by the defect structure ofthe film; thus it can be expected that optimum growth conditions andsurfaces may be different from growth on dislocated material.Unfortunately, obtaining smooth morphology for crystals used for makingLEDs is difficult, especially when GaN material is grown on native bulksubstrates. The surface of GaN material used for manufacturing LEDdevices is often uneven, and usually has miscuts, which are generallythought undesirable for LED devices. The present disclosure takesadvantage of the miscuts and uneven surface of the GaN substrate, asdescribed below. As used herein, “miscut” refers to a surface angle thatis off from the “a-plane,” the “m-plane,” or other crystallographicplane. “Miscut” also refers to the angle between a wafer surface and theclosest high-symmetry/low-index major crystallographic plane, e.g.,c-plane, m-plane, or a-plane.

Certain embodiments provided by the disclosure provide methods forimproving the surface morphology of (Al,Ga,In)N thin films grown on bulk(Al,Ga,In)N substrates. Methods provided by the present disclosure alsoresult in a uniform emission wavelength in layer structures containing(Al,Ga,In)N bulk layers or heterostructures. The obtained smooth(Al,Ga,In)N thin films can serve as a template for the growth of highperformance light emitting and electronic devices. Common vapor phaseepitaxy techniques, such as metalorganic chemical vapor deposition(MOCVD), molecular beam epitaxy (MBE) and hydride vapor phase epitaxy(HVPE), can be used to grow the (Al,Ga,In)N thin films. Certainembodiments provided by the present disclosure, however, are equallyapplicable to (Ga,Al,In,B)N thin films grown by other suitable vaporphase growth techniques.

Disclosed herein are methods for improving the surface morphology of(Al,Ga,In)N thin films grown on bulk substrates by intentionallyemploying miscuts. Improved surface morphology can lead to a number ofadvantages for nitride devices, including improved uniformity in thethickness, composition, doping, electrical properties, and/orluminescence characteristics of the individual layers in a given device.Furthermore, the resulting smooth surfaces lead to significantreductions in optical scattering losses, which is beneficial to theperformance of, for example, laser diodes.

Typically when epitaxy occurs on a miscut surface, a particular plane isexposed at the end of a terrace in a set of terraces. The miscutdirection specifies the plane that is exposed, and for growth on [0001]or [000-1] GaN surfaces, can comprise a superposition of the [1-100] and[11-20] directions. The angle away from normal defines the step density.A miscut toward [1-100], for example, exposes a set of m planes. Smoothsurface morphology can be achieved by growing GaN on a native GaN bulksubstrates having a miscut toward the [1-100] plane (m-direction) of atleast 0.35 degrees. In embodiments wherein a miscut varies across asubstrate or wafer, the minimum off-cut toward the [1-100] directionshould be at least 0.35° degrees. The substrate miscut in the [11-20]direction may vary by a wider margin, for example, from −1 degrees to 1degree, in certain embodiments from −1 degrees to 1.5 degrees, or incertain embodiments greater than from −1.5 degrees to 1.5 degrees.Growth on greater miscut angles may yield rough surfaces characterizedby severe step-bunching that manifests as a ‘rippled’ or ‘wrinkled’surface as shown in FIG. 3 and in FIG. 7. As shown in FIG. 3 and FIG. 7,the fraction of the surface that is composed of ripples is reduced withincreasing miscut angle up to about 0.35 degrees, at which miscut anglesignificant defects are no longer evident.

Certain embodiments provided by the present disclosure include anonpolar or semipolar (Ga,Al,In,B)N film comprising a top surface thatis a nonpolar or semipolar plane, having a planar and optically smootharea, such that the area has an absence of identifiable non-planarsurface undulations or features as measured using an optical microscopeand with light wavelengths between 400 nm and 600 nm, wherein the areais sufficiently large for use as a substrate for epitaxial deposition ofone or more device layers on a top surface of the area, and the devicelayers emit light having an output power of at least 2 milliwatts at 20milliamps (mA) drive current.

FIG. 1 is a simplified representation of the substrate miscut across asubstrate. The substrate shown in FIG. is a bulk GaN substrate. FIG. 1Adepicts the variation of m-miscut or miscut toward the [1-100]direction. FIG. 1B depicts the variation of a-miscut or miscut towardthe [11-20] direction. The miscut angles with respect to the c-plane areshown in the surfaces of the substrates depicted in FIG. 1A and FIG. 1B.As shown in FIG. 1A, miscut angles toward the m-direction range fromabout 0.2 degrees to about 0.7 degrees. In comparison, as shown in FIG.1B, miscuts toward the a-direction range from about −0.65 degrees toabout 1 degrees.

FIG. 2 shows photoluminescence (PL) maps for an InGaN/GaNheterostructure grown on a substrate. The wavelength distribution, PLintensity, and full-width-half-maximum (FWHM) across the wafer arerepresented. One aspect of the substrate performance is wavelengthconsistency, as shown on the top left of FIG. 2 (Peak Lambda 1).Referring to the miscut angles along m-direction shown in FIG. 1, it canbe seen that there is a greater amount of uniformity in wavelength wherethe miscut angle is at least 0.35 degrees. For example, for a miscutangle of 0.35 degrees or greater toward the m-direction, the wavelengthis close to 388.5 nm to 393.6 nm, whereas when the miscut angle is atleast 0.35 degrees, the wavelength can be over 400 nm. As an example,the PL emission wavelength across the substrate, for a fixed a-planemiscut, varies with the m-plane miscut, when the m-plane miscut is lessthan 0.35 degrees. Alternatively, the PL emission wavelength across thesubstrate, for a fixed m-plane miscut is substantially insensitive tothe a-plane miscut. Other PL characteristics such as peak intensity(Peak Int 1), signal intensity (Int. Signal 1) and FWHM across thedevice surface are also provided.

FIG. 3 shows the surface morphology of a device grown on a substrate.The images were obtained by Nomarski microscopy and correspond tovarious locations on the substrate. As can be seen, a wrinkled surfacebecomes visible at the left hand side where the miscut angle along them-direction is less than 0.35 degrees. In contrast, when the miscutangle is at least 0.35 degrees, the winkled surface is less apparent.Therefore, substrate areas having a miscut angle of at least 0.35degrees toward the m-direction can be used to eliminate, reduce, orminimize wrinkled surfaces on bulk gallium and nitrogen containingsubstrates and layers grown on such substrates.

FIG. 4 shows atomic force microscopy (AFM) amplitude or height imagesacross 2 μm×2 μm areas on different parts of a substrate surface. Thecorresponding RMS roughness values (nm) are indicated for certain of theindividual images.

FIG. 5 shows AFM height or amplitude images across 50 μm×50 μm areas ondifferent parts of a substrate surface. The corresponding RMS roughness(nm) is indicated for each of the individual images. At a 50 μm×50 μmlevel, the unevenness is more pronounced (e.g., RMS 6.77 nm) for areaswith a miscut angle less than 0.35 degrees. In contrast, in areas wherethe miscut angle is at least 0.35 degrees, the unevenness is less,ranging from RMS of 0.25 nm to 0.6 nm.

In certain embodiments, methods for fabricating (Al,Ga,In)N thin film onsubstrate areas are provided that have a miscut angle of at least 0.35degrees. Methods also provide a substrate or template with a miscut awayfrom a low index crystal orientation. A (Al,Ga,In)N thin film can begrown directly on a Ga-face (Al,Ga,In)N substrate or template which is amiscut c-plane substrate or template. The substrate or template can be aGa-face c-plane substrate or template, and the miscut angle toward[1-100] direction is at least 0.35 degrees. The resulting surfacemorphology of the (Al,Ga,In)N film is atomically smooth with a RMSroughness of less than 1 nm over at least a 2,500 μm² area of thesurface. In certain embodiments, a RMS roughness of less than 0.2 nmover at least a 2,500 μm² area of the surface has also been observed. Itis to be appreciated that the miscut angle of at least 0.35 degreestoward the m-direction provides wavelength uniformity for a devicefabricated on the surface. In certain embodiments, the standarddeviation of wavelength uniformity across the smooth surface is lessthan 1%, and in certain embodiments, less than 0.2%.

In certain embodiments, the RMS roughness is less than 1 nm over asurface area of at least 500 μm², at least 1,000 μm², at least 1,500μm², at least 2,000 μm², at least 2,500 μm², at least 3,000 μm², atleast 4,000 μm², and in certain embodiments, at least 5,000 μm². Incertain embodiments, the RMS roughness is less than 0.2 nm over asurface area of at least 500 μm², at least 1,000 μm², at least 1,500μm², at least 2,000 μm², at least 2,500 μm², at least 3,000 μm², atleast 4,000 μm², and in certain embodiments, at least 5,000 μm².

In certain embodiments, the substrate or template is an Ga-face c-planesubstrate or template, and the miscut angle toward the [1-100] directionis at least 0.35 degrees, and less than 0.6 degrees, and in certainembodiments, less than 1 degree. When a (Al,Ga,In)N film is grown on asurface of the miscut, the surface morphology of the (Al,Ga,In)N film isatomically smooth with a RMS roughness of less than 1 nm, and in certainembodiments less than 0.2 nm over at least a 2,500 μm² area of thesurface. The wavelength of the emission from a (Al,Ga,In)N containingdevice grown on the surface is substantially uniform across the surface,with a standard deviation of wavelength uniformity less than 1%, and incertain embodiments, as low as less than 0.2%

In certain embodiments, the substrate or template is an Ga-face c-planesubstrate or template, and the miscut angle toward the [1-100] directionis greater than at least 0.35 degrees and less than 0.75 degrees or, incertain embodiments, less than 0.8 degrees. A (Al,Ga,In)N film grown ona surface of the miscut is atomically smooth with a RMS roughness ofless than 1 nm over at least a 2,500 μm² area and in certainembodiments, less than 0.2 nm over at least a 2,500 μm² area of thesurface.

A substrate can also be oriented along the c-plane. In certainembodiments, the substrate or template is a Ga-face c-plane substrate ortemplate, and the miscut angle toward the [11-20] direction is greaterthan −1 degree and less than 1 degree. In certain embodiments, thesubstrate or template is a Ga-face c-plane substrate or template, themiscut angle toward the [1-100] direction of at least 0.35 degrees andless than 0.6 degrees or in certain embodiments, less than 1 degree; andthe miscut angle toward the [11-20] direction is greater than −1 degreeand less than 1 degree. A (Al,Ga,In)N film grown on the surface of themiscut has a surface morphology of the (Al,Ga,In)N with a RMS roughnessof less than 1 nm, and in certain embodiments less than 0.2 nm over atleast a 2,500 μm² of the surface with a standard deviation of wavelengthuniformity less than 1% and in certain embodiments, less than 0.2%.Similar results are achieved when the substrate or template is a Ga-facec-plane substrate or template, with a miscut angle toward the [1-100]direction of at least 0.35 degrees and less than 0.75 degrees or incertain embodiments, less than 0.8 degrees; a miscut angle toward the[11-20] direction greater than −1 degree, and less than 1 degree.

The layers of material can be formed in various ways. The multiple(Al,Ga,In)N layers can be grown successively and can be used to form alight emitting device and/or an electronic device. The layers include n-and p-type doped layers in which at least one active region is formed.

In certain embodiments, the present disclosure provides methods formanufacturing LED diodes from bulk substrate material. The methodsinclude providing a bulk substrate material having a top surface with aregion characterized by a c-plane orientation with a miscut angle of atleast 0.3 degrees or at least 0.35 degrees toward an m-direction. Theregion is diced to form separate members in which LED diodes are formed.

FIGS. 6A-D illustrate substrate materials according to certainembodiments provided by the present disclosure. In FIG. 6A, a bulksubstrate 602 has a cylindrical shape (similar to as single crystalboule) in the [0001] direction 616. To obtain substrates that can beused for manufacturing LED devices, the top surface 604 of the bulksubstrate, which is aligned according to the c-plane 601 (i.e., thecrystallographic [0001] plane), can be used as a reference plane togenerate c-plane wafers 612. Conventional processing techniques include,for example, slicing a bulk substrate along a surface substantiallyparallel to the c-plane 601 to provide an on-axis c-plane wafer 612. Incontrast, certain embodiments provided by the present disclosure use a“miscut angle” surface for the wafer material. As shown in FIG. 6A, thec-plane wafer surface is defined by the a-axis [2110] 606 and the m-axis[0110] 608. In FIG. 6A, a miscut angle 614 of at least 0.35 degreesrelative to the m-axis 608 can be selected to obtain an even and smoothsurface for the wafer material 610 used to manufacture LED devices.

In FIG. 6B, a bulk substrate 602 has a cylindrical shape (similar to assingle crystal boule) in the [0001] direction 611. To obtain substratesthat can be used for manufacturing LED devices, the top surface 604 ofthe bulk substrate, which is aligned according to the c-plane 601 (i.e.,the crystallographic [0001] plane), can be used as a reference plane togenerate c-plane wafers. Conventional processing techniques include, forexample, slicing a bulk substrate along a surface substantially parallelto the c-plane 601 to provide an on-axis c-plane wafer 612. In contrast,certain embodiments provided by the present disclosure use a “miscutangle” surface for the wafer material. As shown in FIG. 6B, the c-planewafer surface is defined by the a-axis 606 and the m-axis [0110] 608. Asshown in FIG. 6B, a miscut angle 614 of at least 0.35 degrees relativeto the a-axis 606 can be selected to obtain an even and smooth surfacefor a wafer material 610.

In FIG. 6C, a bulk substrate 602 has a cylindrical shape (similar to assingle crystal boule) in the [0001] direction 611. To obtain substratesthat can be used for manufacturing LED devices, the top surface 604 ofthe bulk substrate, which is aligned according to the c-plane 601 (i.e.,the crystallographic [0001] plane), can be used as a reference plane togenerate c-plane wafers. Conventional processing techniques include, forexample, slicing a bulk substrate along a surface substantially parallelto the c-plane 601 to provide an on-axis c-plane wafer 612. In contrast,certain embodiments provided by the present disclosure use a “miscutangle” surface for the wafer material. As shown in FIG. 6C, the c-planewafer surface is defined by the a-axis [2110] 606 and the m-axis [0110]608. In FIG. 6C, a miscut angle of at least 0.35 degrees relative toboth the a-axis and the m-axis can be selected to obtain an even andsmooth surface for the wafer material 610.

FIG. 6D provides a schematic cross-sectional view depicting relativeorientation of lattice planes 626 with respect to a wafer surface 624 ina miscut wafer. As can be seen from FIG. 6D, the miscut direction 618normal to the surface 620 is “off” from the crystal plane normal 622.

In certain embodiments, the miscut angle on the c-plane is at least 0.30degrees toward the m-direction, at least 0.32 degrees, at least 0.35degrees, at least 0.37 degrees, at least 0.40 degrees, and in certainembodiments, at least 0.42 degrees.

FIG. 7 shows images for various miscut substrates according to certainembodiments provided by the present disclosure. As shown, there is adecrease in surface roughness at miscut angles of at least 0.35 degreestoward the m-axis.

FIG. 8 shows the relationship of surface roughness to miscut angle forc-plane substrates miscut toward the m-direction and toward thea-direction according to certain embodiments provided by the presentdisclosure. As shown, the surface roughness is dramatically reduced atmiscut angles of at least about 3.5 degrees toward the m-direction.

FIG. 9 shows an example of growth steps for fabricating an opticaldevice according to certain embodiments provided by the presentdisclosure. The optical device shown in FIG. 9 includes a bulk GaNsubstrate 901, which can be miscut as provided herein, a n-type layer902 such as silicon-doped GaN layer, an active region comprising, forexample, multiple quantum wells including active layers 903 and barrierlayers 904, an electron blocking layer 905, and a p-type layer 907 suchas a Mg-doped GaN layer. In certain embodiments, the p-layer comprises asecond p-type layer 906, where p type layer 906 acts as an electronblocking layer and p-type layer 907 serves as a contact area. As shownin FIG. 9, the growth sequence includes depositing at least (1) ann-type epitaxial material; (2) an active region; (3) an electronblocking region; and (4) a p-type epitaxial material. Of course, therecan be other variations, modifications, and alternatives. Furtherdetails of the present method can be found throughout the presentspecification and more particularly below. Examples of certainattributes and deposition parameters for the various materials formingthe layers shown in FIG. 9 are provided as follows:

1. Bulk wafer:

Any orientation, e.g., polar, non-polar, semi-polar, c-plane.

(Al,Ga,In)N-based material

Threading dislocation (TD) density: <1E8 cm⁻²

Stacking fault (SF) density: <1E4 cm⁻¹

Doping: >1E17 cm⁻³

2. N-type epitaxial material:

Thickness: <5 μm, <1 μm, <0.5 μm, <0.2 μm

(Al,Ga,In)N based material

Growth Temperature: <1,200° C., <1,000° C.

UID or doped

3. Active regions:

At least one AlInGaN layer

Multiple Quantum Well (MQW) structure

QWs are >20 Å, >50 Å, >80 Å thick

QW and n- and p-layer growth temperature identical, or similar

Emission wavelength <575 nm, <500 nm, <450 nm, <410 nm

4. P-type epitaxial material

At least one Mg-doped layer

<0.3 μm, <0.1 μm

(Al,Ga,In)N based

Growth T<1100° C., <1000° C., <900° C.

At least one layer acts as an electron blocking layer.

At least one layer acts as a contact layer.

FIG. 10 shows an example of steps for growing a rectifying p-n junctiondiode according to certain embodiments provided by the presentdisclosure As shown in FIG. 10, the growth sequence includes depositingat least (1) an n-type epitaxial material 1002; and (4) a p-typeepitaxial material 1003. In certain embodiments, bulk GaN substrate 1001includes a (Al,Ga,In)N-based substrate with any orientation such as amiscut orientation disclosed herein, a threading dislocation densityless than 1E8 cm⁻², a stacking fault density less than 5E3 cm⁻¹ and adoping greater than 1E17 cm⁻³. In certain embodiments, n-layer 1002 is(AlGaIn)N-based such as n-GaN. In certain embodiments, n-layer 1002 hasa thickness less than 2 μm, less than 1 μm, less than 0.5 μm, and incertain embodiments, less than 0.2 μm. In certain embodiments, n-layer1002 is grown at a temperature less than 1200° C. and in certainembodiments, less than 1000° C. In certain embodiments, n-layer 1002 maybe unintentionally doped or doped. The device shown in the upper portionof FIG. 10 shows an example of a device comprising a bulk GaN substrate,an n-type layer 1002 such as a Si-doped AlInGaN layer, and a p-typelayer 1003, such as a Mg-doped AlInGaN layer.

FIG. 11 shows an example of a simplified growth method for forming ahigh electron mobility transistor or a metal-semiconductor field effecttransistor according to certain embodiments provided by the presentdisclosure. As shown, the growth sequence includes depositing at least(1) an unintentionally doped epitaxial material (buffer); and (4) an(AlInGaN) barrier material, which is either unintentionally doped orn-type doped. In certain embodiments, bulk GaN substrate 1101 includes a(Al,Ga,In)N-based substrate with any orientation such as a miscutorientation disclosed herein, a threading dislocation density less than1E8 cm⁻², a stacking fault density less than 5E3 cm⁻¹ and a dopinggreater than 1E17 cm⁻³. In certain embodiments, buffer layer 1102 is(AL,Ga,IN)N-based such as n-GaN. In certain embodiments, buffer layer1102 has a thickness less than 2 μm, less than 1 μm, less than 0.5 μm,and in certain embodiments, less than 0.2 μm. In certain embodiments,buffer layer 1102 is grown at a temperature less than 1200° C. and incertain embodiments, less than 1000° C. In certain embodiments, bufferlayer 1102 comprises a single layer rendered semi-insulating by Fe or Cdoping. In certain embodiments, buffer layer 1102 is unintentionallydoped. In certain embodiments, a barrier layer has a thickness less than0.1 μm, less than 500 nm, and in certain embodiments, less than 30 nm.In certain embodiments, the barrier layer is (Al,Ga,In)N-based such asAlGaN, which may be doped with Si or unintentionally doped. In certainembodiments, the barrier layer is a single layer. In certainembodiments, the barrier layer is grown at a temperature of less than1200° C., less than 1100° C., and in certain embodiments, less than1000° C. As shown at the top of FIG. 11, in certain embodiments, adevice may be a HEMT or a MESFET, comprising, for example, a bulk GaNsubstrate 1101, an unintentionally doped GaN buffer layer, and anunintentionally doped or Si-doped AlGaN barrier layer.

Although the above disclosure is primarily directed to LED devices, itwill be appreciated that the methods and materials can be applied to thefabrication and processing of other electronic and optoelectronicdevices. As an example, certain embodiments provided by the presentdisclosure can be applied using an autocassette MOCVD reactor where thecassette holds two or more single wafers or wafer platters formulti-wafer reactors. In certain embodiments, an epitaxial structure canform an LED device capable of emitting electromagnetic radiation in arange of 390-420 nm, 420-460 nm, 460-450 nm, 500-600 nm, and others. Incertain embodiments, various devices can be fabricated using methods,substrates, and materials provided by the present disclosure including,for example. p-n diodes, Schottky diodes, transistor, high electronmobility transistors (HEMT), bipolar junction transistors (BJT),heterojunction bipolar transistors (HBT), metal-semiconductor fieldeffect transistors (MESFET), metal-oxide-semiconductor field effecttransistors (MOSFET), metal-insulator-semiconductor heterojunction fieldeffect transistors (MISHFET), and combinations of any of the foregoing.In certain embodiments, a gallium and nitrogen containing material usedas a substrate can be characterized by one or various surfaceorientations, e.g., nonpolar, semipolar, polar.

Finally, it should be noted that there are alternative ways ofimplementing the embodiments disclosed herein. Accordingly, the presentembodiments are to be considered as illustrative and not restrictive.Furthermore, the claims are not to be limited to the details givenherein, and are entitled their full scope and equivalents thereof.

What is claimed is:
 1. A device comprising; a bulk (Al,Ga,In)Nsubstrate; a plurality of epitaxial layers overlying the bulk(Al,Ga,In)N substrate and defining a light-emitting device structure,wherein a top surface of the device structure is characterized by anominal c-plane crystallographic orientation miscut by an angle from0.35 degrees to 1 degrees toward an m-direction; and wherein theepitaxial layers of the light-emitting device structure are configuredto have a standard deviation of photoluminescent wavelength uniformityof less than 1% over at least a 2,500 μm² area.
 2. The device of claim1, wherein: the epitaxial layers of the light-emitting device structureare configured such that the top first surface is characterized by aroot mean square surface roughness of less than 1 nm over the at least2,500 μm² surface area.
 3. The device of claim 2, comprising at leastone n-type doped layer overlying the bulk (Al,Ga,In)N substrate.
 4. Thedevice of claim 3, comprising at least one active region overlying theat least one n-type doped layer.
 5. The device of claim 4, wherein thetop surface is characterized by a nominal Ga-face c-planecrystallographic orientation miscut by an angle from 0.35 degrees to 1degrees toward a <1-100> direction, and by an angle from −1 degree to 1degree toward a <11-20> direction.
 6. The device of claim 4, comprisingat least one p-type doped layer overlying the at least one activeregion.
 7. The device of claim 4, wherein the at least one active layercomprises AlInGaN.
 8. The device of claim 1, wherein the top surface ischaracterized by an RMS surface roughness from 0.25 nm to 0.6 nm over atleast a 2,500 μm² surface area.
 9. The device of claim 1, wherein thetop surface is characterized by a RMS surface roughness less than 0.2 nmover at least a 2,500 μm² area.
 10. The device of claim 1, wherein thedevice structure is characterized by a standard deviation ofphotoluminescent wavelength uniformity is less than 1% over at least a2,500 μm² surface area.
 11. The device of claim 1, wherein the devicestructure is characterized by a standard deviation of photoluminescentwavelength uniformity is less than 0.2% over at least a 2,500 μm²surface area.
 12. The device of claim 1, wherein the miscut angle isfrom 0.35 degrees to 0.8 degrees toward the m-direction.
 13. The deviceof claim 1, wherein the top surface is further characterized by a miscutangle from −1 degrees to 1 degree toward a <11-20> direction.
 14. Thedevice of claim 1, wherein the device comprises a light emitting diode.15. The device of claim 14, wherein the light emitting diode ischaracterized by an output power of at least 2 milliwatts at 20milliamps drive current.
 16. The device of claim 1, wherein the bulk(Al,Ga,In)N is bulk GaN.
 17. The device of claim 1, wherein the devicecomprises a wafer.
 18. A semiconductor device fabricated from the waferof claim 17.